In general, in the case of applying a coating, for instance, diluted coating and nondiluted coating, to a web of plastic film, paper or cloth, the phenomenon that the coating escapes from the surface being coated to the opposite surface of the web must be prevented.
Therefore so far the coating has been applied only to a portion whose width is shorter than the overall width of the web.
For instance, in the case of coating a web 1 with a wire bar 2 as shown in FIG. 1, reduced-diameter portions or steps 3 are formed at both of the end portions of the wire bar 2 so that the coating width w of the wire bar 2 is shorter than the overall width W of the web 1.
When the web 1 is sufficiently thick in thickness, no problem arises with the wire bar 2 with the stepped portions 3. But when the web 1 is considerably thin in thickness and, for instance, is 2-9.mu. in thickness, longitudinal wrinkles are produced on the surface of the web 1 at the portions thereof in contact with both of the stepped portions 3 of the wire bar 2 so that no satisfactory coating can be obtained.
In a prior art gravure coating device of the type shown in FIG. 2, when a coating is applied to a thin web, longitudinal wrinkles are produced on the surface of the thin web. The reason why such longitudinal wrinkles are produced is as follows. A coating applied to a gravure roll 5 is transferred to the under surface of a web 1 which is extended by extension rolls 4 and clamped under a suitable pressure between the gravure roll 5 and a rubber roll 6. As a result, when the web 1 is thin, longitudinal wrinkles are produced on the surface of the web 1 because of the clamping pressure. In FIG. 2, reference numeral 7 designates a doctor blade: and 8, a pan for storing a coating.
The same problem is encountered when a gravure coating device of the type as shown in FIG. 1 of U.S. Pat. No. 4,438,695 granted to Maier et.al. and a gravure coating device of the type as shown in FIG. 1 of U.S. Pat. No. 4,474,110 granted to Rosner are used.